Device and method for melt spinning fine non-woven fibers

ABSTRACT

A meltblown method for melt spinning fine non-woven fibers and a device for carrying out said method. According to the invention, a polymer melt is extruded, in order to form several fiber strands, through several nozzle bores of a spinning nozzle and twisted on the outlet side of the nozzle bores by means of a cold blow flow. According to the invention, the blow flow is fed to the fiber strands in an acceleration path wherein the fiber stands and the blow flow are accelerated in such a manner that the fiber strands are twisted in order to form continuous fine fibers. According to the inventive device, the inventive acceleration path is formed between the upper edges and the lower edges of the two blow nozzle openings below the spinning nozzle.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of international applicationPCT/EP 2004/014403, filed 17 Dec. 2004, and which designates the U.S.The disclosure of the referenced application is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The invention relates to a melt-blown method for melt spinning finenon-woven fibers, as well as to a device for carrying out said method.

In the production of non-woven microfibers a plurality of fiber strandsare extruded from a polymer melt through nozzle holes of a spinneret andthen drawn with a blowing stream into microfibers. Such fibers exhibitan average fiber diameter of usually <10 μm. In the state of the artsuch methods are called melt-blown methods. The blowing stream ispreferably produced from hot air that is blown with a high expenditureof energy on the fiber strands. The blowing stream leads to drawing andbursting of the fiber strands so that fine non-woven fibers of finitelength are produced.

DE 33 41 590 A1 and corresponding U.S. Pat. No. 4,526,733 disclose sucha method, where a fluid, which is not heated up, is used as the blowingstream. In principle, such relatively cold blowing streams exhibit theadvantage that there is no need to heat up the fluid. This method couldalso produce fine fibers made of thermoplastic polymers, which exhibit afineness of less than 10 μm.

Irrespective of whether the prior art melt-blown method is carried outwith a hot blowing medium or with a cold blowing medium, as disclosed inthe DE 33 41 590 A1, the fiber strands are usually torn into finitefibers. In addition to the disadvantageous formation of fuzz, suchfibers lead, upon being deposited to form a non-woven fabric, toirregularities in the physical properties due to the conglutinated fiberpieces. In particular, such non-woven fabrics can tolerate only slighttensile strengths owing to the finite fiber pieces.

DE 199 29 709 A1 discloses another method for producing fine non-wovenfibers. In this method the fiber strands are split into fine fibers bymeans of a gas stream. The prior art method, which is referred to as theNanoval method in professional circles, is based on generating apressure effect on the fiber strand subject to the action of a gasstream and a nozzle unit. Said pressure effect causes the fiber strandto burst so that a plurality of fine, essentially endless fibers isproduced. At the same time the hydrostatic pressure, prevailing in theinterior of the fibers, is greater than the gas pressure that envelopsthe fiber strands and by means of which the bursting of the fiberstrands is achieved. Then the fibers are guided—subject to the action ofthe gas stream—to a depositing area and are deposited as a non-wovenfabric.

All of the state of the art melt-blown methods run the risk that theindividual fibers will conglutinate before the final solidification andlead to undesired points of discontinuity in the non-woven fabric.

Therefore, an object of the invention is to provide a melt-blown methodfor melt spinning fine non-woven fibers of the type described in theintroductory part. According to this method, a high quality microfibercould be produced at a relatively low expenditure of energy.

Another goal of the invention is to provide non-woven fibers forproducing a non-woven fabric, which exhibits improved physicalproperties.

In addition, an object of the invention is to improve a melt-blownmethod and a melt-blown device for melt spinning fine non-woven fibersin such a manner that a microfiber is produced that exhibits maximumuniformity and continuity in order to attain, during their subsequentmanufacture into a non-woven fabric, a uniform distribution of thefibers during the depositing process.

SUMMARY OF THE INVENTION

The above objectives and others are realized according to the inventionby providing, in one embodiment, a method for melt spinning finenon-woven fibers, comprising extruding a polymer melt through severalnozzle holes of a spinneret in order to form several fiber strands, andimmediately after emerging from the nozzle holes, acting on the fiberstrands with a cold blowing stream that, subject to the action of anoverpressure, flows through at least one blowing nozzle orifice onto thefiber strands and draws the fiber strands, wherein the blowing stream isguided to the fiber strands inside an acceleration section, in which thefiber strands and the blowing stream are accelerated in such a mannerthat the fiber strands are drawn to form infinite microfibers. Thepresent invention also provides a non-woven fiber and a resultingnon-woven fabric produced according to the method.

The invention is based on the knowledge that in the conventionalmelt-blown methods, the blowing stream is accelerated, upon impinging onthe fiber strand, to a maximum velocity. Therefore, the meeting of theblowing stream and the fiber strand results in a more or less suddenelongation of the fiber strands. This elongation leads to draftingand—optionally upon exceeding a maximum spinning draft—to tearing of thefibers. In order to avoid such overstressing of the fibers, the blowingstream is fed, according to the invention, to the fiber strands insidean acceleration section. In the acceleration section the blowing streamand the fiber strands are then accelerated together in such a mannerthat the fiber strands are drawn to form endless micro fibers. In thisway overstressing the fiber strand while drawing can be avoided in anadvantageous way. The maximum velocity of the blowing stream is notreached until the end of the acceleration section and leads to thedesired total drawing of the fiber strands.

Since the blowing stream and the fiber strands are accelerated insidethe acceleration section, the blowing stream can be fed to the fiberstrands at a relatively low expenditure of energy. Thus, it has beendemonstrated that merely an overpressure in a range below 1,000 mbar issufficient to provide the fiber strands with the desired spinning draft.Consequently the consumption of the blowing stream can also be reducedto a minimum.

The blowing stream is preferably air that exhibits a natural airtemperature in a range between 15° C. and 110° C. Thus, it is possibleto quickly establish peripheral zones for the fibers, a feature thatbenefits in particular the stability of the fibers for drawing. Inaddition, the microfibers cool better. In this respect it is importantthat the air does not heat up. Therefore, the temperature that acceptsthe air without cooling or heating owing to the environmental conditionsis called here the natural air temperature.

The blowing stream is produced preferably from the surrounding air at anambient temperature. Said surrounding air is drawn in from theenvironment below the spinneret. At an average consumption ofapproximately 600 m³/h*m of surrounding air and at a maximumoverpressure of 1 bar in a conventional spinning device, the blowingstream can be provided at a low cost.

Owing to the alternative method, with which the fiber strands areextruded at a mass flow of the polymer melt through the nozzle hole ofthe spinneret of 1.0 g/min. to 10 g/min. per nozzle hole, all of thecurrent types of polymers, for example polypropylene or polyamide, maybe extruded. Preferably a throughflow of >3 g/min. is set per nozzlehole. Therefore, the hole diameter may lie in a range between 0.2 and1.0 mm.

Therefore, it is especially advantageous for the polymer melt to beheated inside the spinnerets just before emerging from the nozzle holes,so that the freshly extruded fiber strand exhibits a relatively highmelting temperature that may be, for example, above 350° C. for apolypropylene fiber. Depending on the type of polymer, the polymer meltis heated preferably to a range between 300° C. and 400° C. in order toobtain a constant optimal setting as a function of the type of polymer,the capillary diameter of the nozzle holes and the desired fiberfineness, the length of the acceleration section for accelerating theblowing stream and the fiber strands ranges from 2 mm to 30 mm.

Thus, the fiber strands can be fed directly from the nozzle hole intothe acceleration section or not until the fiber strands have passedthrough a short extrusion zone of a maximum 2 mm, in which the fiberstrands may emerge from the nozzle hole without any influence of theblowing stream.

In order to generate high draft forces on the fiber strands, a preferredalternative of the method provides that the fiber strands and theblowing stream are fed, upon passing through the acceleration section,into a free space, where an atmosphere prevails that is in essence equalto an ambient pressure. The expansion of the blowing stream into thefree space produces zones of turbulence, which improves the blowingstream's attack on the fiber surface. So-called whiplash effects mayalso occur with the result that the fibers continue to be drawn.

In order to intensify such effects, additional zones of air turbulencemay be generated by air conductors inside the free space. This in turnalso generates special effects in the fibers, such as thick and thinpoints.

However, there is also the possibility of providing an additional airstream inside the free space for the purpose of cooling. Thisalternative of the method is especially advantageous to implement inthose cases, in which the blowing stream exhibits relatively high airtemperatures.

The method, according to the invention, is suitable for processing allcurrent types of polymers, such as polypropylene, polyethylene,polyester or polyamide, and to process into non-woven fibers withmicrofiber cross sections ranging up to 0.5 μm. In particular, goodresults could be attained with a polypropylene material, where the fiberfineness of the infinite microfibers was in a range between 1 μm and 30μm.

The microfiber, produced with the method according to the invention, issuitable, as an infinite fiber, in particular for depositing in order toform a non-woven fabric.

The inventive device for carrying out the inventive method provides thatan acceleration section is formed between the upper edges and the bottomedges of the two blowing nozzle orifices, which are arranged below thespinneret. Thus, there is no need for any additional aids in order toachieve an acceleration section, which is designed directly below thenozzle holes. The device, according to the invention, is characterizedin particular in that a plurality of fiber strands can be drawnuniformly with relatively close spacing to form microfibers without theadjacent fibers conglutinating. Therefore, the device, according to theinvention, is suitable for producing a large number of high qualitymicrofibers of high uniformity.

According to an advantageous further development of the inventivedevice, the upper edge of the two blowing nozzle orifices is assigned toan entry throat; and the bottom edges of the two blowing nozzle orificesare assigned to an exit throat in order to achieve a definedacceleration section. The exit throat exhibits a free flow cross sectionthat is smaller than the flow cross section of the entry throat. Thus,after the fibers have passed through the entry throat, they may beaccelerated continuously by means of the blowing stream, emerging fromthe blowing nozzle orifices, as far as up to the exit throat.

Depending on the fiber fineness and the type of polymer, the exit throatis set to a slit width ranging from 2 to 8 mm. The slit width is definedby the smallest distance between the bottom edges that are opposite eachother and belong to the blowing nozzle orifices.

The entry throat, which exhibits a larger slit width, can be formedadvantageously directly on a level with the underside of the spinneret,so that the extruded fiber strands can enter directly into theacceleration section. However, there is the possibility of forming theentry throat at a short distance from the underside of the spinneret, sothat the fiber strands do not reach the acceleration section until afterpassing through a short extrusion zone ranging from 0 to 2 mm.

The length of the acceleration section is defined by the distance of theentry throat from the exit throat. Depending on the type of fiber andthe fiber fineness this length may range from 2 mm to 20 mm.

A preferred design of the inventive device exhibits an inflow channelfor each blowing orifice for the air supply. Said inflow channel isformed between the bottom edge and the upper edge of the respectiveblowing nozzle. Therefore, the upper edge and the bottom edge arealigned or formed in such a manner that the inflow channel exhibits inthe direction of the blowing orifice a tapering flow cross section onthe end of the bottom edge and the upper edge respectively. Thus, acontinuous acceleration of the supplied air as far as up to the entryinto the acceleration section can be achieved so that a small supply ofenergy is necessary to generate the blowing stream.

The air that is made available is held advantageously in reserve in apressure chamber that is connected to the blowing orifices.

According to an especially advantageous further development of theinventive device, the pressure chamber is connected to a suction unit inorder to provide air as inexpensively as possible. This suction unittakes in the surrounding air and conveys it directly into the pressurechamber.

A free space is formed below the bottom edges of the blowing orifices inorder to facilitate an intensive draft of the fiber strands during theexpansion of the blowing stream upon emerging from the accelerationsection.

The free space may contain additional aids for guiding, cooling and/ordrawing the fibers. This gives the inventive device a high degree offlexibility that makes it possible to produce microfibers of any typeand for any application.

The non-woven fiber, which is made of a polymer material and producedaccording to the method of the invention, is characterized in that,despite the microfiber cross sections ranging from 0.5 μm to 30 μm, thefibers exhibit an infinite length. This makes it possible to provideinfinite microfibers, produced by a melt-blown method, in order toproduce non-woven fabrics.

Thus, the inventive non-woven fabric, which is formed from the non-wovenfibers of the invention, is characterized in particular by a highuniformity both in the machine direction and in the cross direction.Therefore, such non-woven fabrics are especially suitable for barrierproducts, where, on the one hand, permeability to air is desired, but,on the other hand, such a non-woven fabric exhibits a blocking effectwith respect to liquids. Therefore, the inventive non-woven fabric isespecially suitable for hygienic products, medical products and filterapplications.

The inventive non-woven fabric is characterized in particular by ahigher stretching ability as compared to conventional melt-blownnon-woven fabrics. Therefore, the inventive non-woven fabric can be usedadvantageously in products, where minor deformations occur duringproduction or use. In particular for such applications a suitablenon-woven fabric is one, where the infinite microfibers, which are madeof a polypropylene, are deposited to form a weight per unit of area in arange between 1.5 g/m² and 50 g/m² and lead to an elongation at break ofat least 60% or can tolerate a maximum tensile stress at an elongationof at least 40%.

The high strength and deformability of the non-woven fabrics make itpossible to produce in an advantageous manner composite non-wovenfabrics that exhibit a plurality of layers. In the composite non-wovenfabric of the invention, at least one of the layers is made of anon-woven fabric exhibiting the infinite microfibers of the invention.

Both the inventive non-woven fabric and the composite non-woven fabricare especially suitable for hygienic products, such as diapers, sanitarynapkins, medicinal products, such as wound dressings, filter products,or household products, such as cleaning cloths or dust cloths.

Therefore, for the above applications in particular composite non-wovenfabrics, wherein at least one other layer is made of a spun bondnon-woven fabric, are preferably used.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a schematic representation of a view of one embodiment of theinventive device for carrying out the inventive method;

FIG. 2 is a schematic representation of a view of a detail of thespinneret underside of another embodiment of the inventive device;

FIG. 3 is a schematic representation of a view of a detail of anotherembodiment of the inventive device;

FIG. 4 is a schematic representation of a longitudinal sectional view ofanother embodiment of the inventive device;

FIG. 5 is a diagram of the elongation as a function of the weight perunit of area of a non-woven fabric, according to the invention; and

FIG. 6 is a diagram of the tensile strength as a function of the weightper unit of area of a non-woven fabric, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, the present inventionmay be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein; rather, these embodimentsare provided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

FIG. 1 is a schematic representation of a view of a first embodiment ofthe inventive device for carrying out the inventive method.

The embodiment exhibits a spinneret 1, which is connected to a meltsource (not illustrated here) by means of a melt feed 2. Usually anextruder is used as the melt source. Said extruder melts a thermoplasticmaterial and feeds said material as the polymer melt under pressure tothe spinneret. The underside of the spinneret 1 exhibits a plurality ofnozzle holes 5, which are connected inside the spinneret 1 to the meltfeed 2. The nozzle holes 5 are configured on the underside of thespinneret 1 in a specific arrangement, preferably in a series of rowswith one or more rows next to one another. A fiber strand can beextruded out of the polymer melt emerging from each of the nozzle holes5.

Underneath the spinneret 1 there is a blower 3, which exhibits twoblowing nozzles 4.1 and 4.2, which lie opposite each other and arelocated a short distance underneath the spinneret 1. Each of the blowingnozzles 4.1 and 4.2 contains a blowing nozzle orifice 7.1 and 7.2, whichis formed between a respective upper edge 9.1 or 9.2 and the respectivebottom edge 10.1 or 10.2. The upper edge 9.1 and/or 9.2 and the bottomedge 10.1 and/or 10.2 are designed in the shape of plates and extendwith their free end essentially parallel to the nozzle holes 5 of thespinneret 1. Thus, the upper edges 9.1 and 9.2, which lie opposite eachother, form an entry throat; and the bottom edges 10.1 and 10.2, whichlie opposite each other, form an exit throat for the fiber strands 6.The entry throat and the exit throat are designed in such a manner thatbetween the upper edges 9.1 and 9.2 and the bottom edges 10.1 and 10.2there is an acceleration section 15, in which a blowing stream, emergingfrom the blowing nozzle orifice 7.1 and 7.2, is accelerated togetherwith the fiber strands 6.

The upper edges 9.1 and 9.2 of the blowing nozzles 4.1 an 4.2 areusually arranged in such a manner with respect to the spinneret 1 that,on the one hand, no significant heat losses can occur at the spinneret 1and, on the other hand, no blowing air can escape outside theacceleration section. The design (which is not shown in FIG. 1) of thetransition from the spinneret 1 to the upper edges 9.1 and 9.2 shall beexplained in detail below.

Each of the blowing nozzles 4.1 and 4.2 is assigned a pressure chamber8.1 and 8.2, in which is stored a blowing medium, which is held under anoverpressure. Preferably air is used as the blowing medium. However, itis also possible to use a gas. The pressure chambers 8.1 and 8.2 may beconnected jointly or separately to a pressure source, for example acompressed air ductwork system. Below the blower 3 there is a free space12 that extends from the bottom edges 10.1 and/or 10.2 of the blowingnozzles 4.1 and 4.2 as far as to a depositing belt 13. The depositingbelt 13 serves to deposit the drawn microfibers 11 to form a non-wovenfabric 14. To this end, the depositing belt 13 is connected to a drivein order to carry away in a continuous mode the non-woven fabric 14after the microfibers 11 have been deposited. The arrows show thedirection of movement of the depositing belt 13.

The embodiment (shown in FIG. 1) of the inventive device is shown in anoperating situation. When in operation, the spinneret 1 is fedcontinuously a polymer melt, which is made, for example, ofpolypropylene. The spinneret 1 is designed so that it can be heated inorder to hold the melt temperature of the polymer melt in a range above300° C., preferably in a range between 300 and 400° C. Then the polymermelt is extruded through the nozzle holes 5 to form a respective fiberstrand 6. After the fiber strands 6 emerge from the nozzle holes 5, theyarrive in the acceleration section 15 and are brought together with ablowing stream. Thus, the fiber strands 6 and the blowing stream areaccelerated continuously inside the acceleration section 15 as far as upto an exit throat. In this way the fiber strands 6 are increasinglystretched. The result is that following the expansion of the blowingstream in the free space, said fiber strands form microfibers with afiber cross section in a range between 0.5 μm and 30 μm. Then themicrofibers 11 are deposited continuously as the non-woven fabric 14 onthe depositing belt 13.

A cold blowing medium, preferably cold air, is used as the blowingmedium for taking off and stretching the fiber strands 6. This processallows the fiber strands to cool down until they are deposited, so thatno additional cooling of the fibers is necessary. At air temperaturesof, for example 25° C., in particular the free space 12 between theblower 3 and the depositing belt 13 can be held extremely small so thatthe blowing stream significantly improves the depositing of themicrofibers so as to form a non-woven fabric. In addition, the stabilityof the fiber guide is enhanced in that, when the cold blowing air meetsthe freshly extruded fiber strands, rapid cooling of the peripheralzones of the fiber strands 6 takes place. However, the stretchabilityremains essentially preserved owing to the molten core areas of thefiber strands 6.

In order to attain maximum draft forces by means of the blowing stream,the blowing nozzles 4.1 and 4.2 are formed preferably in such a mannerthat the blowing stream already flows out of the blowing nozzle orificesin the direction of travel of the fibers. To this end, FIG. 2 is a crosssectional view of another embodiment of the inventive device. This crosssectional view shows only a part of the spinneret underside with theunderlying blowing nozzle orifices of the blowing nozzles.

The detail in FIG. 2 shows the emergence situation of a fiber strand 6at the spinneret 1 in a cross sectional view. To this end, the spinneret1 exhibits a nozzle hole 5. The spinneret 1 has a number of heatingelements 19 in order to heat the polymer melt, conveyed inside thespinneret 1.

Below the spinneret 1 there are blowing nozzles 4.1 and 4.2 with blowingnozzle orifices 7.1 and 7.2. The blowing nozzle orifice 7.1 is placedbetween the upper edge 9.1 and the bottom edge 10.1. The upper edge 9.1and the bottom edge 10.1 are designed as mold plates, which betweenthemselves form the inflow channel 18.1. The inflow channel 18.1exhibits a flow cross section that tapers off in the direction of theblowing nozzle orifice 7.1 so that the blowing air, supplied inside theinflow channel 18.1, is accelerated continuously as far as up to theblowing nozzle orifice 7.1. At the same time the inflow channel 18.1 isshaped by the upper edge 9.1 and the bottom edge 10.1 in such a mannerthat the blowing stream, emerging from the blowing nozzle orifice 7.1,is fed in the direction of travel of the fibers. It has proven to beespecially advantageous if the upper edge 9.1 in relation to the bottomedge 10.1 exhibits such a physical curvature that its theoreticalimaginary extension that projects beyond the free end strikes in themiddle of an exit throat 17, which is formed by the bottom edges 10.1and 10.2, which lie opposite each other. At the same time, thecontinuous decrease in the distance between the upper edge 9.1 and thebottom edge 10.1 continues as far as up to the middle of the exit throat17. This design of the blowing nozzle 4.1 makes it possible to improvethe accelerating effect for drawing off the fiber strand.

The blowing nozzle orifice 7.2 of the blowing nozzle 4.2 on the oppositeside of the spinneret 1 is identical (as the mirror-image) to the firstblowing nozzle orifice 7.1 of the blowing nozzle 4.1. The inflow channel18.2 between the formed plates of the upper edge 9.2 and the bottom edge10.2 is configured with a tapering flow cross section. Thus, withrespect to a more detailed description reference is made to theaforesaid.

The upper edges 9.1 and 9.2 are spaced apart so as to lie opposite eachother below the underside of the spinneret 1 and form an entry throat16. The slit width of the entry throat 16 is labeled with the capitalletter E in FIG. 2 and defined by the distance between the two upperedges 9.1 and 9.2. The slit width E is essentially constant over theentire spinning width of the spinneret 1.

Below the upper edges 9.1 and 9.2 the bottom edges 10.1 and 10.2 arearranged so as to lie opposite each other in relation to the exit throat17. The slit width of the exit throat 17 is labeled with the capitalletter A in FIG. 2 and is defined by the narrowest distance between thetwo bottom edges 10.1 and 10.2. The slit width A of the exit throat 17is also in essence constant over the entire spinning width of thespinneret 1. The slit width A of the exit throat 17 is designed smallerthan the slit width E of the entry throat 16. Between the entry throat16 and the exit throat 16 there is an acceleration section 15. Inparticular, through the inflow channels 18.1 and 18.2, which belong tothe blowing nozzles 4.1 and 4.2 and which empty directly into theacceleration section 15, the fiber strand 6 together with the blowingair is guided from the entry throat 16 with increasing velocity alongthe acceleration section 15 as far as up to the exit throat 17 and blowninto the free space 12, which is formed below the exit throat 17. Thedistance between the entry throat 16 and the exit throat 17, whichdefines directly the exit cross section of the blowing nozzle orifices7.1 and 7.2 and gives the length of the acceleration section 15, mayrange from 2 mm to 30 mm as a function of the type of polymer and fiberfineness. The split width of the exit throat 17 varies from 2 mm to 8mm. Even if the nozzle holes 5 exhibit a capillary diameter of 0.6 mm,microfibers exhibiting a fiber fineness in a range between 1 and 30 μmcould be produced with the device of the invention.

On the side of the blowing nozzles 4.1 and 4.2 that faces the spinneret1, a sealant 23.1 and 23.2 is disposed between the spinneret 1 and theupper edges 9.1 and 9.2. The sealants 23.1 and 23.2 form, on the onehand, in relation to the spinneret 1 an insulating layer in order toavoid heat losses and, on the other hand, a seal with respect to theblowing air, conveyed in the acceleration section 15. The sealants 23.1and 23.2 are made preferably of insulating materials.

In the embodiment of the inventive device, depicted in FIG. 2, there isspace between the underside of the spinneret 1 and the accelerationsection 15. The result of this space is that the fiber strands 6 do notenter the acceleration section until after they have passed through ashort extrusion zone. Such a reverse movement leads to an additionalstability with respect to the travel of the fiber strands.

However, it is also possible to let the extruded fiber strands 6 passinto the acceleration section 15 directly after leaving the nozzle holes5. Such an embodiment of the inventive device is depicted as a schematicrepresentation in a sectional view in FIG. 3. The design of thespinneret 1 as well as of the blowing nozzles 4.1 and 4.2 is in essenceidentical to the above embodiment, according to FIG. 2, so thatreference is made to the above description, and only the differences areexplained.

The entry throat 16 between the upper edges 9.1 and 9.2 is constructeddirectly on a level with the underside of the spinneret 1. The result isthat upon leaving the nozzle hole 5, the fiber strands 6 enter directlyinto the acceleration section 15 and make contact with the blowingstream and thus acquire from the spinneret 1 a different take-offbehavior.

On the side of the blowing nozzles 4.1 and 4.2 that faces the spinneret1, there is one respective air gap 24.1 and 24.2 between the spinneret 1and the upper edges 9.1 and 9.2. The air gaps 24.1 and 24.2 aredimensioned so closely that in essence no blowing air can pass through,but a sufficient layer of air remains in order to insulate it from thespinneret 1.

In order to improve and increase the drawing of the microfibers 11, thefree space 12 in the embodiment, depicted in FIG. 3, has a number ofconductors 20, which result in the formation of a plurality ofturbulence zones and, thus, effect an intensification of the drawingprocess. However, this enables the production of even preferablymicrofibers with special effects, such as thin points.

FIG. 4 shows a schematic representation of a longitudinal sectional viewof another embodiment of the device of the invention. The embodiment,according to FIG. 4, is in essence identical to the embodiment accordingto FIG. 1, so that only the differences are explained below, andotherwise reference is made to the above description.

In the embodiment, depicted in FIG. 4, the blower 3 exhibits a suctionunit 21 below the spinneret 1. The suction unit 21 is connected to thepressure chambers 8.1 and 8.2. The suction unit 21 takes in thesurrounding air from below the spinneret 1 and feeds it to the pressurechambers 8.1 and 8.2. In this way, the blowing stream for drawing thefiber strands can be produced advantageously from the surrounding air.Thus, the surrounding air exhibits a room temperature that may range, asa function of the surroundings, from 15° C. to 40° C. Thus, the resultis that the blowing stream can be provided and produced at a very lowcost.

The embodiment, depicted in FIG. 4, exhibits an injector 22 in order tofurther improve the guide of the fibers below the blowing nozzles 4.1and 4.2 in the free space 12.

Therefore, when the fiber strands pass through the injector 22, thesurrounding air pending in the free space 12 from the surrounding, isdirectly involved without any outside assistance in the guiding andcooling of the fibers. However, it is also possible forclimate-controlled air to be drawn into the free space 12. Then, as theconditioned air, the climate-controlled air can be predetermined withrespect to the air temperature, humidity and air quantity so thatspecific cooling conditions at the fibers can be set. However, suchmechanisms are used preferably in those cases, in which the blowingstream must be produced from a relatively warm air.

In principle, the inventive method and the inventive device for carryingout the inventive method are suitable for use with polymer melts of allcurrent polymers, such as polyester, polyamide, polypropylene orpolyethylene.

In one example of the method, a polymer, which is made of apolypropylene, is melted to form a melt and extruded through a nozzlehole having a capillary diameter of 0.6 mm and a melt throughput of 6g/min. per nozzle hole. The number of nozzle holes was 36. The pressurechambers 8.1 and 8.2 were supplied with air at room temperature and anoverpressure of 260 mbar. Therefore, the configuration of the device,depicted in FIG. 2, was used in order to draw the extruded fiber strandsso as to form microfibers. After extruding and drawing, the PPmicrofibers were deposited to form a non-woven fabric with a weight perunit of area of 50 g/m². An analysis of a non-woven fabric samplerevealed a fiber fineness of the microfiber in a range between 2.5 and25.1 μm. The average fiber cross section of the microfibers was 5.2 μm.The subsequent determination of the elongation at break of a non-wovenfabric sample, which was 40 mm long, yielded a value of 63% in themachine direction and 70% in the cross direction. At the same time amaximum tensile strength of 29 N in the machine direction and 17 N inthe cross direction could be determined. Therefore, in comparison withconventional melt-blown non-woven fabrics with finite fiber pieces, anapproximately 300% improvement in the physical properties could bedetermined.

In a series of experiments the polypropylene fibers were deposited toform non-woven fabric that exhibited a variety of different weights perunit of area. The results are plotted in the diagram in FIG. 5 and FIG.6. The diagram, shown in FIG. 5, shows the relationship between theweight per unit of area of the non-woven fabric and the attainedelongation at break. The capital letters MD and CD designate theorientation of the non-woven material, where MD (machine direction)stands for the machine direction and CD (cross direction) stands for thecross direction in the non-woven fabric. As the weight per unit of areadecreases, the elongation at break increases, an effect that indicatesin particular the high strength of the infinite microfibers. Compared tothe conventional melt-blown non-woven materials, an increase of up to300% with respect to the elongation at break could be determined.

FIG. 6 shows a diagram of the tensile strength of the non-woven fabricas a function of the weight per unit of area. Here, too, a significantincrease over the conventional melt-blown non-woven fabrics could bedetermined. The maximum tensile strength was above 5 N for non-wovenmaterials with a weight per unit of area of about 10 g/m² and above 25 Nfor non-woven materials with a weight per unit of area of about 50 g/mirrespective of the direction of pull. Therefore, such non-wovenmaterials are especially suitable for applications, where deformations,such as in hygienic materials, must be tolerated, or where deformationsoccur during production. The microfiber characteristics of the non-wovenfabric, according to the invention, result, on the one hand, in an airand/or vapor permeability with a simultaneous low penetration tendency.Thus, the non-woven materials can be used preferably as barrierproducts, such as in the hygiene sector for diapers and sanitarynapkins. However, applications in medical technology, such as wounddressings, are also possible.

The non-woven fabrics, made of such fibers, may be included in anespecially advantageous manner in composite materials. The suctioncapability and blocking effect of such non-woven fabrics may be usedadvantageously in a composite non-woven fabric in order to form abarrier layer.

The significantly high elongation and tensile strength of the inventivemelt-blown method also lead to improved processing. Even applicationswith small deformation, such as in hygienic products, are possiblewithout any problems.

Many modifications and other embodiments of the invention set forthherein will come to mind to one skilled in the art to which thisinvention pertains having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the invention is not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. A melt-blown method for melt spinning fine non-woven fibers,comprising: extruding a polymer melt through several nozzle holes of aspinneret in order to form several fiber strands; and immediately afteremerging from the nozzle holes, acting on the fiber strands with a coldblowing stream that, subject to the action of an overpressure, flowsthrough at least one blowing nozzle orifice onto the fiber strands anddraws the fiber strands, wherein the blowing stream is guided to thefiber strands inside an acceleration section, in which the fiber strandsand the blowing stream are accelerated in such a manner that the fiberstrands are drawn to form endless microfibers.
 2. The method as claimedin claim 1, wherein the overpressure of the blowing stream is set to avalue of less than or equal to about 1,000 mbar.
 3. The method asclaimed in claim 1, wherein the blowing stream is produced from air thatexhibits a natural air temperature in a range between about 15° C. andabout 120° C.
 4. The method as claimed in claim 3, wherein the blowingstream is produced from the surrounding air at an ambient temperature,the surrounding air being drawn in from the environment below thespinneret.
 5. The method as claimed in claim 1, wherein the fiberstrands are extruded at a mass flow of the polymer melt through thenozzle holes of the spinneret in the range of about 1.0 g/min. to about10 g/min. per nozzle hole.
 6. The method as claimed in claim 5, whereinthe mass flow is greater than about 3 g/min. per nozzle hole.
 7. Themethod as claimed in claim 1, wherein before emerging from the nozzlehole, the polymer melt is heated to a temperature in a range betweenabout 300° C. and about 400° C.
 8. The method as claimed in claim 1,wherein a length of the acceleration section for accelerating theblowing stream and the fiber strands ranges from about 2 mm to about 30mm.
 9. The method as claimed in claim 8, wherein the accelerationsection adjoins directly the mouth of the nozzle holes without anyspacing.
 10. The method as claimed in claim 8, wherein the accelerationsection adjoins directly the mouth of the nozzle holes at a shortdistance in the range of a maximum of about 2 mm.
 11. The method asclaimed in claim 1, wherein after passing through the accelerationsection, the fiber strands and the blowing stream are fed into a freespace, the free space exhibiting a pressure that is approximately equalto the ambient pressure.
 12. The method as claimed in claim 11, whereinadditional zones of air turbulence, acting on the fibers, are generatedby at least one air conductor inside the free space.
 13. The method asclaimed in claim 1, wherein the fibers are cooled and guided by means ofan air stream, supplied below the acceleration section.
 14. The methodas claimed in claim 1, wherein a fiber fineness of the endlessmicrofibers lies in a range between about 0.5 μm and about 30 μm. 15.The method as claimed in claim 1, wherein the microfibers are depositedto form a non-woven fabric.
 16. A device for melt spinning finenon-woven fibers, the device comprising: a spinneret, the underside ofwhich exhibits a plurality of nozzle holes configured in rows; and ablower, which exhibits two blowing nozzle orifices, which lie oppositeeach other, each of the blowing nozzle orifices being formed between anupper edge and a bottom edge, both of which extend substantiallyparallel to the nozzle holes, wherein an acceleration section is formedbetween the upper edges and the bottom edges of the two blowing nozzleorifices below the spinneret, and wherein in the acceleration sectionthe fiber strands and the blowing stream are accelerated in such amanner that the fiber strands are drawn into endless microfibers. 17.The device as claimed in claim 14, wherein an exit throat is formedbetween the bottom edges of the two blowing nozzle orifices, and anentry throat is formed between the upper edges of the two blowing nozzleorifices, wherein the exit throat exhibits a free flow cross sectionthat is smaller than a flow cross section of the entry throat.
 18. Thedevice as claimed in claim 15, wherein an exit throat exhibits a slitwidth in a range between about 2 mm and about 8 mm.
 19. The device asclaimed in claim 17, wherein the entry throat is constructed on a levelwith the bottom side of the spinneret.
 20. The device as claimed inclaim 17, wherein the entry throat is constructed at a short distancefrom the bottom side of the spinneret.
 21. The device as claimed inclaim 17, wherein the entry throat and the exit throat define the lengthof the acceleration section, which lies in a range between about 2 mmand about 30 mm.
 22. The device as claimed in claim 14, wherein thebottom edge and the upper edge, which are assigned to one of the blowingorifices, form between themselves an inflow channel for the air feed,and wherein the inflow channel in the direction of the blowing orificeexhibits a tapering flow cross section.
 23. The device as claimed inclaim 16, wherein the blowing orifices are connected to at least onepressure chamber, in which the air is held under overpressure.
 24. Thedevice as claimed in claim 23, wherein the pressure chamber is connectedto a suction unit, by means of which surrounding air is drawn in andconveyed into the pressure chamber.
 25. The device as claimed in claim16, wherein a free space is formed below the bottom edges of the blowingnozzles.
 26. The device as claimed in claim 25, wherein the free spaceexhibits additional aids for at least one of guiding, cooling, ordrawing the fibers.
 27. Non-woven fibers made of a polymer material andproduced by means of a melt-blown method as claimed in claim 1, themicrofibers comprising an endless length, whereby a fiber fineness ofthe endless microfibers lies in a range between about 0.5 μm and about30 μm.
 28. A non-woven fabric made of non-woven fiber, the fibersproduced by means of a melt-blown method as claimed in claim 1 andexhibiting an endless length, whereby a fiber fineness of the endlessmicrofibers lies in a range between about 0.5 μm and about 30 μm. 29.The non-woven fabric as claimed in claim 28, wherein the endlessmicrofibers are deposited to form a weight per unit of area in a rangebetween about 1.5 g/m² and about 50 g/m² and lead to an elongation atbreak of at least about 60%.
 30. A composite non-woven fabric,comprising several layers of non-woven fabric, wherein at least one ofthe layers is made of a non-woven fabric exhibiting the endlessmicrofibers as claimed in claim
 24. 31. The composite non-woven fabricas claimed in claim 30, wherein the non-woven fabric of the layerexhibits a weight per unit of area in a range between about 1.5 g/m² andabout 50 g/m² and exhibits an elongation at break of at least about 60%.32. The composite non-woven fabric as claimed in claim 30, wherein atleast one other layer is made of a spun bond non-woven fabric.